1. Field of the Invention
The present invention relates to an exhaust gas cleaning apparatus having a particulate collector for use in an automotive vehicle.
2. Description of Related Art
Recently, an exhaust gas cleaning apparatus having a collector for collecting particulates exhausted from a diesel engine has been used. The collector is made of ceramics having plural small passages through which exhaust gas from a diesel engine flows. Particulates contained in the exhaust gas adhere to walls separating the small passages, and thereby the particulates are trapped in the collector. As an amount of particulates trapped in the collector becomes large, a pressure loss in the collector increases. The amount of accumulated particulates is estimated based on a pressure difference measured at upstream and downstream ends of the collector.
When the estimated amount of accumulated particulates reaches a predetermined level, the accumulated particulates are burnt to regenerate the collector. More particularly, fuel (unburned hydrocarbon) is supplied to an oxidizing catalyst contained in the collector by means of a post injection (a fuel injection performed after a main injection, not to contribute to generation of power). By oxidizing the hydrocarbon, a temperature in the collector is increased to thereby burn the accumulated particulates.
On the other hand, if the collector is damaged due to dropping-off or melting-down of a downstream portion of the collector, the pressure difference between the upstream end and the downstream end of the collector becomes smaller than a normal pressure difference. Accordingly, such damages in the collector are detected based on the pressure difference. An example of this kind of damage detection device is disclosed in JP-A-2003-155920. In this device, however, it is difficult to correctly detect the damages in the collector based on the pressure difference because changes in the pressure difference are not large enough when an amount of exhaust gas is small.